Tropical Storm ROSA

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TROPICAL STORM ROSA DISCUSSION NUMBER   7
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP172012
200 PM PDT WED OCT 31 2012
 
VISIBLE SATELLITE IMAGES AND MICROWAVE DATA SHOW THAT THE CENTER OF
ROSA REMAINS ON THE WESTERN EDGE OF A LARGE AREA OF DEEP
CONVECTION. SATELLITE INTENSITY ESTIMATES ARE 45 KT FROM TAFB AND
SAB...WITH A RECENT ASCAT PASS SHOWING MAXIMUM WINDS OF ABOUT 40
KT. THUS THE INITIAL INTENSITY REMAINS 45 KT. WESTERLY VERTICAL
WIND SHEAR IS EXPECTED TO SIGNIFICANTLY INCREASE TOMORROW...WHICH
SHOULD INDUCE WEAKENING. THIS SCENARIO HAS BEEN WELL ADVERTISED BY
THE LARGE-SCALE AND REGIONAL GUIDANCE...AND THE LATEST NHC FORECAST
IS BASICALLY AN UPDATE OF THE PREVIOUS ONE. STRONG VERTICAL SHEAR
STILL SHOULD CAUSE ROSA TO DEGENERATE INTO A REMNANT LOW BY DAY 4.

THE INITIAL MOTION OF ROSA IS ESTIMATED TO BE ABOUT 260/3...WITH THE
ASCAT AND OTHER MICROWAVE DATA SHOWING PRETTY CLEARLY THAT THE
STORM HAS BEEN MOVING A BIT SOUTH OF WEST TODAY. THE TROPICAL
CYCLONE REMAINS CAUGHT WITHIN LIGHT STEERING BETWEEN A MID-LEVEL
HIGH LOCATED NEAR 130W AND FLAT TROUGHING NORTH OF ROSA. OTHER THAN
ACCOUNTING FOR A SLIGHT SOUTHWARD RELOCATION OF THE CENTER...THE
FORECAST TRACK OF ROSA IS BASICALLY UNCHANGED DURING THE NEXT DAY
OR SO. THE MODEL GUIDANCE FROM THIS CYCLE IS EERILY SIMILAR TO THE
PREVIOUS PACKAGE WITH A HUGE DISPARITY BETWEEN THE BEST PERFORMING
MODELS. THE KEY TO THE FORECAST COULD LIE IN THE EVOLUTION OF A
SIGNIFICANT CUTOFF LOW THAT IS PREDICTED BY MOST OF THE GUIDANCE TO
FORM WEST OF BAJA CALIFORNIA IN A FEW DAYS. THE MODELS THAT FORM A
STRONGER LOW FASTER...SUCH AS THE GFS/GFDL/HWRF...SHOW ROSA TURNING
TOWARD THE NORTH BEYOND DAY 3 AS IT GETS CAUGHT BY THE TROUGH.
HOWEVER...ANOTHER CAMP OF MODELS...INCLUDING THE ECMWF/UKMET/GEFS
MEAN AND FSU SUPERENSEMBLE...SHOW A SLOWER AND MORE POSITIVELY
TILTED TROUGH...WHICH CAUSES ROSA TO SHEAR OUT SOONER AND CONTINUE
MOVING WESTWARD. THE GEFS AND ECMWF ENSEMBLE MEMBERS SUPPORT THE
WESTWARD MODEL SOLUTIONS...AND THE OFFICIAL FORECAST CONTINUES TO
LEAN IN THAT DIRECTION. 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  31/2100Z 14.2N 117.9W   45 KT  50 MPH
 12H  01/0600Z 14.3N 118.2W   45 KT  50 MPH
 24H  01/1800Z 14.3N 118.6W   40 KT  45 MPH
 36H  02/0600Z 14.2N 118.8W   35 KT  40 MPH
 48H  02/1800Z 14.0N 119.0W   35 KT  40 MPH
 72H  03/1800Z 13.8N 119.6W   30 KT  35 MPH
 96H  04/1800Z 14.5N 120.5W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  05/1800Z 15.5N 121.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 
$$
FORECASTER BLAKE
 
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